A large body of evidence suggests that genetic factors predispose to the development of obesity. Recent work from several laboratories has begun to elucidate the molecular basis of several forms of genetic obesity in rodents. We have initiated a project to extend the work emanating from the positional cloning of the murine obese gene. The obese gene encodes leptin, a peptide hormone secreted by adipose tissue. We have obtained cDNA clones encoding human and mouse leptin, and have also immunized rabbits with GST-fusion proteins to obtain anti-leptin antisera. Using these reagents, we have initiated various studies into the regulation of leptin secretion. Because of the crucial role of dietary state upon leptin secretion, we have inquired whether there is acute hormonal regulation of leptin secretion. When adipose tissue is incubated in vitro, insulin can be demonstrated to increase the rate at which leptin is secreted. Furthermore, morphologic studies suggest that insulin alters the subcellular localization of leptin in isolated adipocytes. These changes are consistent with the interpretation that leptin secretion is regulated directly in addition to the regulation due to the action of hormones to regulate the transcription of the leptin gene. In separate experiments, we obtained cDNA clones encoding various isoforms of the leptin receptor. The availability of these reagents have enabled us to initiate studies into the structure and function of leptin receptors, and to explore their physiologic roles in regulating appetite and metabolism.